MOS transistors (such as power MOSFETs or IGBTs) can be switched on and off by charging and discharging the gate of the transistor. In order to control the transition between a non-conductive (off-state) and a conductive state (on-state), and vice versa, a gate-resistor is usually connected to a gate electrode of the transistor. The resistance of the gate-resistor limits the gate current that charges or discharges the gate. For charging and discharging the gate capacitor of power MOS transistors, dedicated gate driver circuits (or simply gate drivers) are used. Such gate drivers charge and discharge the gate in response to one or more logic signals (binary signals) which may represent the desired switching state (on or off) of the transistor.
In some applications it is desired to have different gate current values for charging and, respectively, discharging the gate of a MOS transistor. Different gate current values for charging and discharging the gate result in an asymmetric switching, i.e., the switching times are significantly different for switching transistor on and off. Such an asymmetric switching behavior may be achieved, for example, by using appropriately designed gate driver circuits. Such gate drivers usually require a relatively complicated circuit design. Furthermore, various undesired effects may occur due to unavoidable parasitic circuit components present within such gate driver circuits. Thus there is a need for an improved MOS transistor which allows asymmetric switching without the need for sophisticated gate driver circuits.